Most homeowners understand that their central air conditioning system makes a certain amount of noise while running. Unfortunately, there’s not much anyone can do about that. However, here at Fire 'n' Ice Heating & Cooling, Inc., we often field questions from baffled homeowners asking us why their AC system continues to make noise even after it turns off. Some of the answers to that question are no cause for concern. Others, however, are.

1. The Condensate Pump Is Still Running

One of the most common reasons an AC system keeps making noise after it turns off is that its condensate pump continues to run. It will produce a buzzing sound that you might hear if your home’s quiet. The condensate pump removes water from the drip pan beneath your AC’s evaporator coils. The good news is that it’s not unusual for a condensate pump to keep running after the AC turns off.

There’s a simple way to check whether the condensate pump is the noise source. Once your AC turns off and the noise starts, go outside your home and look at the end of the system’s drain line. You should see a constant drip of water coming from it. When the noise eventually stops, wait about 5 minutes and check again. If the dripping stopped, the noise you heard was almost certainly the condensate pump.

2. You hear Ductwork Expansion or Contraction

Another noise you could hear when your AC isn’t running is the sound of your home’s ductwork expanding or contracting. Such sounds aren’t uncommon. Often, they’re the result of your AC pressurizing the ductwork while it operates, which pushes the aluminum walls of the ducts outward. When your AC turns off, the ducts will contract back into their original shape. The process can sound like a popping or banging noise.

The same could happen if you have a temperature differential between the air in the ducts and the outside. This can cause the metal in the ductwork to contract while your AC runs and then expand again once your AC shuts off. In both cases, the sounds aren’t anything to worry about and are little more than an annoyance. If it’s too bothersome, it could be possible for an HVAC technician to lower your AC’s fan speed or adjust some of the dampers in your ductwork to eliminate the noise.

3. You hear Motorized Dampers Closing

If your home has a multi-zone AC system, another noise you might hear after the system turns off is the motorized dampers in your ductwork snapping shut. Some multi-zone systems return their motorized dampers to their default closed position after the system turns off. Closing dampers may make a slamming or snapping sound moments after your AC turns off.

This is another sound that you shouldn’t worry about. It’s a sign that your multi-zone AC is working as intended. The only exception is if you hear the sound repeatedly while the system’s off. Once the dampers close, they should stay that way until the system turns on again. If they’re not, it might result from a malfunction somewhere.

4. A Failing Contactor Relay Switch

The final common reason that an AC might make noise while it’s off is also the only one that should concern you. Its noises are related to electrical problems with your AC system. One of the frequent causes of this is a failing contactor relay switch. It’s a component located in your AC’s outdoor unit, and it controls the power flow to the compressor and fan motor inside the outdoor unit. When it begins to fail, it could emit a loud buzzing sound even while your AC isn’t running.

The good news is that a qualified HVAC technician can replace a failing contactor switch fairly easily. And if you catch the problem in time, it shouldn’t result in any other damage to your AC system. If you don’t, however, the switch could heat up and cause harm to other nearby components. So, if you hear a buzzing sound coming from anywhere in your AC system’s outdoor unit, don’t ignore it and contact the experts at Fire 'n' Ice Heating & Cooling, Inc. right away.

The team here at Fire 'n' Ice Heating & Cooling, Inc. has the experience and expertise to track down and solve any problems with your AC that result in odd noises. We specialize in HVAC installation, repair, and maintenance and even offer comprehensive air quality solutions. So, if you hear any odd noises from the air conditioner in your Downers Grove area home, contact Fire 'n' Ice Heating & Cooling, Inc. for an AC maintenance appointment today!

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